Polymer composition having terminal alkene and terminal carboxyl groups

ABSTRACT

A polymer composition comprising a urethane having terminal unsaturation and a terminal carboxyl group and which is capable of further free radical polymerization has been synthesized. This polymer can be a liquid or a solid depending on the molecular weight and backbone of the polymer. This polymer as a liquid has been found to be very useful in producing printed circuit boards by photo resist processes.

This application is a division of application Ser. No. 225,809 filedJan. 16, 1981 now U.S. Pat. No. 4,422,914.

This invention relates to a new polymer composition and the use of thispolymer composition alone and in conjunction with other materials as aphoto resist. More particularly, it has been found that a urethanepolymer having terminal unsaturation at one end and a terminal carboxylgroup at the other end is very useful in making printed circuit boardsby etch or plate resist processes and can also be used as a solder mask.

In making a printed circuit board by dry film photo resist methods, asolid photo sensitive material is adhered to the printed circuit boardblank. An image bearing negative of the desired circuit is placed onthis photo sensitive material and the photo sensitive material exposedto light. The light, on striking certain areas of the photo sensitivematerial, changes it so that the material which has not been exposed tothe light and that which has been exposed exhibit differingcharacteristics, such as solubility. The unexposed photo sensitivematerial is the usually removed from the circuit board blank. There arethen left areas coated with a solid polymer and areas uncoated. Theuncoated areas can be coated with solder or the underlying conductivematerial can be removed. The solid polymer remaining on the circuitboard is then usually removed in a subsequent step.

The usual wet photo resist methods for making printed circuit boardsconsist of screen printing a liquid polymer composition onto the circuitboard blank and then exposing the blank to radiation sufficient to cureand solidify the polymer. The cured polymer is then available to protectthe underlying metal layer during one or more of the subsequentprocessing steps. Where a small number of printed circuit boards of aparticular design are to be made, hand screen printing is used. Whenlarge numbers of a given circuit design are to be made, machine screenprinting of the desired circuit design is used.

The essence of photo resist processes is the use of a material whichafter exposure to light can be removed from certain parts of the circuitboard blank, but not from other areas. The material must also be capableof sharp resolution, i.e., it must be a material where the exposed areasand the unexposed areas are clearly and sharply defined. In order to getthis sharp definition, those in the prior art have previously used solidphoto sensitive compositions, and in the instances where a liquid wascoated onto a circuit board blank, it was dried before any imaging. Onereason for using a solid or a dried material was that it was felt thatthe image of the desired circuit had to be in direct contact with thephoto resist in order to get sharp definition in the final circuit.However, this has been found not to be the case. It is possible to havean air gap between the negative or other image of the circuit and thephoto resist and still produce printed circuits with sharp definition.This discovery has led to the feasible use of liquid polymers as photoresists.

These polymers also have uses other than as photo resists. They can beused as protective coatings, and particularly in areas subject tograffiti in the nature of spray painting or liquid pencil notations ordrawings. If a surface which has been treated with these polymers andcured, is subsequently coated with spray paint and pencil art, thepolymer coating, along with the spray paint and pencil, can be removedby a caustic stripping. This is but exemplary of a way these polymerscan be used for other than a photo resist.

In brief summary, the polymer which has been synthesized is a urethanewhich has terminal alkene unsaturation and a terminal carboxyl group.This polymer has the general formula: ##STR1## wherein R₁ is hydrogen,methyl or ethyl, R₂ is an alkyl group of from 1 to 6 carbon atoms, R₃ isthe diisocyanate moiety and can be alicyclic, aryl, alkyl or arylalkylin structure and R₄ is alkyl, alkylene, aryl or alkyl or hydroxysubstituted aryl, and (PE)_(x) is a polyester and/or polyether chainextender unit where X is an integer of from 2 to 50. The terminalbifunctionality of this polymer is very unique in that it makes possiblemany uses, and in particular, the use as a photo resist. In use as aphoto resist, the terminal alkene group provides the capability for freeradical polymerization while the carboxyl group provides forstripability using alkaline solutions. That is, the same molecular unitis curable by actinic light radiation, and after being cured, issusceptable to stripping using alkaline solutions.

These polymers can be synthesized in various ways. However, a preferredroute is to react a diisocyanate with an hydroxy terminated acrylate ormethacrylate to form a monoisocyanate urethane adduct. This acrylate ormethacrylate provides the terminal alkene unsaturation of the finalpolymer composition. The urethane adduct with terminal alkeneunsaturation and a terminal isocyanate is then reacted with a chainextending polyester and/or polyether to produce an hydroxyl terminatedurethane. It is also contemplated to use polyester-polyether mixtures.This reaction consumes the remaining isocyanate content of the urethaneadduct. The hydroxyl terminated urethane is then reacted with ananhydride which provides the terminal carboxyl group of the polymer.When the anhydride is an unsaturated anhydride such as maleic anhydride,there is produced unsaturation α to the carboxyl group.

In more detail, these alkene and carboxyl terminated polymers have amolecular weight in the range of about 250 to 10,000 and an acid contentof about 0.1 to 4.0 meg/g. In synthesizing these polymers, anydiisocyanate which can produce a polymer having the above generalstructure can be used. This diisocyanate has the general formulaR(NCO)₂, where R is a polyvalent organic moiety free from reactivecarbon to carbon unsaturation. Preferred diisocyanates arehexamethylenediisocyanate, toluene diisocyanate, xylylene diisocyanate,diphenylmethane diisocyanate, phenylene diisocyanate, naphthalenediisocyanate, Hylene W, isophorone diisocyanate. The hydroxy terminatedacrylate or methacrylate which is reacted with the diisocyanate isutilized to provide the terminal alkene unsaturation of the polymer.Other than that the hydroxy group must be available for reaction withthe diisocyanate any hydroxyalkyl acrylate or hydroxyalkyl methacrylatecan be used. Non-limiting examples of useful hydroxy terminatedacrylates and methacrylates are hydroxyethyl acrylate, hydroxypropylacrylate, hydroxybutyl acrylate, hydroxyisobutyl acrylate,hydroxyisopentyl acrylate, hydroxyhexyl acrylate, and hydroxyethylmethacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate,hydroxyisobutyl methacrylate, and hydroxypentyl methacrylate.

The diisocyanate and the hydroxy terminated acrylate or methacrylate arereacted. A catalyst is preferably used in the reaction and can beadmixed with the diisocyanate. Suitable catalysts are urethane catalystsuch as dibutyl tin dilaurate or stannous octoate. A catalyst promotorsuch as an organic phosphite can also be used. The hydroxy terminatedacrylate or methacrylate is added slowly to the diisocyanate and theexotherm is controlled so that the temperature of the mixture does notexceed about 85° C., and preferably does not exceed about 70° C. Thereaction is complete when essentially all of the hydroxyl groups of theacrylate or methacrylate have been reactively consumed. This point canbe checked by titrating a sample of the reacted solution withdibutylamine to determine the remaining isocyanate content of thediisocyanate.

After it is determined that the required amount of isocyanate contenthas been consumed, a polyester and/or polyether is added. This polyesteror polyether function primarily as a chain extender and can be anypolyester or polyether having a molecular weight of about 250 to 10,000.The polyester and polyether can have essentially any structure as longas it contains an hydroxyl group which is reactive with the remainingisocyanate group of the diisocyanate and an hydroxyl group which isreactive with an anhydride such as maleic anhydride. Suitable chainextending polymers are poly (diethyleneglycol adipate), poly (ethyleneglycol adipate), poly (ethylene oxide), poly (propylene oxide), poly(tetra methylene oxide), poly (ethylene oxide-propylene oxide)copolymer, poly (nonamethylene oxide), poly (caprolactone) and poly(trimethylolpropane-propylene oxide). There are yet many otherpolyethers and polyesters which could be used in the synthesis of thepresent polymers. The only requirement is that the polyester orpolyether have the reactive capability at one end to undergo reactionwith an isocyanate group, and at the other end, have the reactivecapability to undergo reaction with a cyclic anhydride.

A sufficient amount of chain extending polymer is added to reactivelyconsume the remaining isocyanate group. Since this is a urethanereaction any suitable urethane catalyst such as that used in thereaction of the hydroxy terminated acrylate or methacrylate with thediisocyanate, can be used.

This reaction mixture is maintained at about 50° C. to 90° C., andpreferably about 65° C. to 70° C. for about 4 to 8 hours. Reaction ofthe remaining diisocyanate group is then complete. The degree ofreaction completion can be determined by titration. The polymer moleculeat this stage has terminal unsaturation at one end and a terminalhydroxyl on the other. This terminal hydroxyl group is reacted with acyclic anhydride, such as maleic anhydride, succinic anhydride,citraconic anhydride, tetrahydrophthalic anhydride and hexahydrophthalicanhydride, to cap that end of the polymer with a carboxyl group. When ananhydride such as maleic anhydride is used, the polymer will haveunsaturation α to the carboxyl group. Preferably an esterificationcatalyst such as dibutyl tin dilaurate is used to promote reaction.Stannous octoate, tertiary amines such as triethyl amine or any otheresterification catalyst can also be used. The reaction mixture ismaintained at about 50° to 90° C. until the anhydride content of thereaction mixture has been exhausted. This point of completion ofreaction can be determined by infrared analysis. The polymer product hasan acid content of about 0.1 to 4 meg/g. Whether the synthesized polymerwill be a liquid or a solid is determined by the chain length andmolecular weight of the--(PE)_(x) -- unit and the structure of thediisocyanate.

In a modification of the process for making polymers, suitable for useas a photo resist, an additive copolymer can be synthesized along withthe polymer. Suitable additive copolymers are carboxy terminatedacrylates and methacrylates. These additive copolymers aid in thecontrol of the urethane polymer viscosity and in control of thestripping ease of the cured polymer. These have the general formula:##STR2## where R₄ is hydrogen, methyl or ethyl and R₅ is alkyl of from 1to 6 carbon atoms and R₆ is alkyl, alkylene, aryl or alkyl or hydroxysubstituted aryl. Most conveniently, this additive copolymer is preparedby co-synthesizing it along with the polymer. This is carried out byadmixing an hydroxy alkyl acrylate or methacrylate with partiallysynthesized polymer prior to the final step of reaction with theanhydride. Preferred hydroxy alkyl acrylates and methacrylates arehydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate,hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutylmethacrylate. In this modification the anhydride is added to cap thepolymer and to react with the hydroxyalkyl acrylate or methacrylate. Inthe reaction sequence, the anhydride will react with the hydroxyl groupof the hydroxyalkyl acrylate or methacrylate and with the hydroxyl groupof the urethane polymer being synthesized. The result is that bothmolecules have the same bifunctionality and, as such, are highlycompatable. This co-synthesis also produces a very intimately intermixedpolymer.

In yet another modification of the process for making these polymers acompound to modify the hardness of the cured alkene and carboxyterminated polymer can be co-synthesized along with the alkene andcarboxy terminated polymer. Such compounds have the general formula:##STR3## wherein, R₁, R₂, and R₃ are the same as for the alkene andcarboxy terminated polymer. In order to co-synthesize this compound, thereactant concentrations of diisocyanate and of the hydroxy terminatedacrylate or methacrylate in the step of synthesizing the alkene andcarboxy terminated polymer are adjusted so as to produce the desiredamount of the above compound. That is one additional mole ofdiisocyanate and two additional moles of hydroxy terminated acrylate ormethacrylate are added in the first step of the above describedpreferred reaction sequence.

Considering the various reactants which can be used to make the presentalkene and carboxy terminated polymers, it is not unexpected that thevarious polymers besides being photopolymerizable and stripable usingalkaline solutions, would exhibit other properties. However, it was notexpected that there could be produced a readily photopolymerizable andalkaline stripable hot melt composition. That is, a polymer compositionwhich can be melted and applied to a substrate as a melt, cooled to asolid, and selectively contacted with actinic light to cure the polymerin certain areas. The uncured polymer can be removed by means of analkaline rinse or heating the substrate to melt the uncured polymer sothat it can be removed as a liquid. Such hot melt polymers have thefollowing general structure: ##STR4## wherein R₁, R₂, --PE)_(x) and R₄each have the same meaning as set forth above. In essence the discoverywith regard to hot melt compositions resides primarily in the use ofhexamethylene diisocyanate as the reactive diisocyanate.

In the use of these alkene and carboxyl terminated polymers asphotopolymerizable compositions a photoinitiator is used along with theactinic light for polymerization. Useful photoinitiators arebenzophenone, acetophenone, acenaphthenequinone, o-methoxybenzophenone,dibenzosuberone, anthraquinone, hexanophenone and 2,2 dimethoxy-2-phenylacetophenone. Further, any other photoinitiator which would promote freeradical polymerization of the acrylate group could be used.

Depending on the specific intended use for the alkene and carboxyterminated polymers other materials besides those already set out areused. For instance if it is desired to thicken the polymer to make ascreen-printable ink a thickening agent such as talc, Modaflow, Syloid,Cabosil or Aerosil is added. Other additives which can be incorporatedinto the compositions are epoxy acrylates, multifunctional acrylates,such as hexanediol diacrylate, a multifunctional thiol such aspentaerythritol-tetra-kis (B-mercaptopropionate) and a phenolicstabilizer such as hydroquinone mono-methyl-ether or trihydroxy benzene.These additives serve to stabilize the composition and also providemeans for bridging the polymerized carboxy terminated acrylate to itselfand also to the alkene unsaturation of other components.

In the use of these alkene and carboxyl terminated polymers as photoresist compositions the polymer composition which includes aphotoinitiator is coated onto the metal clad circuit board blank by anyof the usual wet processing techniques. That is, the polymer compositioncan be thickened and applied to parts of the circuit board blank byscreen printing, or it can be applied to the full circuit board blankand in a later step be selectively imaged. When the polymer compositionis screen printed onto the circuit board blank it need only be exposedto actinic light to cure and solidify the polymer to create the photoresist. This cured polymer then protects the underlying metal during thesubsequent plate resist or etch resist processing steps.

When the polymer composition is coated onto the full circuit board blankit is then selectively imaged in a subsequent step in order to cure thepolymer in certain areas to a solid while the polymer which is notexposed remains liquid. This selective curing is accomplished by placinga photo tool, usually a negative of a circuit design, which has opaqueareas and transparent areas above the coated surface. Actinic light isthen focused onto the photo tool, passes through the photo tool in thetransparent areas, and cures the polymer which it contacts to a solid.The polymer which is not contacted by the light remains liquid and isremoved by wiping or by an alkaline wash. This cured polymer is firmlyattached to the metal of the circuit board blank and protects theunderlying metal during the subsequent plate resist or etch resistprocessing steps.

Whether screen printing or any other wet technique is used the curedpolymer is stripped from the surface which it protects is the samemanner. This consists of contacting the circuit board blank with analkaline solution which contains cations derived from a strong base.These are solutions which contain cations which are reactive with thecarboxyl group of the polymer. Suitable alkaline solutions are thosewhich contain sodium, potassium or ammonium ions. Sodium hydroxide in aconcentration of about 2 to 10 percent by weight is a preferredstripping solution.

Various modifications can be made to the present polymers, their methodof synthesis, such as the reaction step sequence, or in the ways theycan be used. However, any such modifications are within the skill of onein the art in view of the disclosures in this application for patent.

The following examples set forth the present invention in more detail:

EXAMPLE I

This example sets forth a process for making one of the preferred liquidpolymer compositions.

A resin kettle is fitted with a stirrer, thermometer, drying tube and anaddition funnel. 185 g of toluene diisocyanate (a mixture of 2,4 toluenediisocyanate and 2,6 toluene diisocyanate), 0.63 g of hydroquinonemonomethyl ether (MEHQ); 5.8 g of triphenyl-phosphite and 0.15 g ofdibutyl-tin dilaurate are added to this kettle. Upon heating the mixtureto 30°-35° C., there is added dropwise 189 g of hydroxypropyl acrylate,allowing the mixture to exotherm to 65° C. The temperature is maintainedbetween 60°-65° C. for 11/2 hours at which time substantially all of thehydroxy groups are consumed, and the NCO content reaches 1.77±0.1 meg/gas determined by titration with dibutylamine. Thereafter, 785 g of poly(diethyleneglycol adipate) with a molecular weight of 1000 is addedalong with 0.15 g of dibutyltin dilaurate catalyst. The reaction mixtureis held at 65° to 70° C. for approximately 3 hours until all theisocyanate groups are consumed.

385 g of hydroxyethyl methacrylate and 0.42 g of hydroquinone are thenadded to this mixture. When the reaction mixture has become uniform andthe temperature has dropped to below 65° C., 248 g of solid maleicanhydride and 8 g of dibutyl-tin dilaurate are added. Slowly (over aboutan hour) the reaction mixture is heated up to 55° C. to dissolve themaleic anhydride. The heating is continued and held at 75° to 80° C. forapproximately 6 hours until the maleic anhydride is completely reacted,as indicated by the absence of 1845 and 1975 cm⁻¹ peaks in an IRspectrograph. The final product thus obtained is a viscous liquid havingviscosity of 5700 cps at 25° C. and acid group contents of 1.4 meq/g.

The prepolymer has the following composition: ##STR5## along with##STR6##

EXAMPLE II

This example sets forth a process for making one of the preferred liquidpolymer compositions.

A resin kettle is fitted with a stirrer, thermometer, drying tube and anaddition funnel. 177.4 g of toluene diisocyanate (a mixture of B 2,4toluene diisocyanate and 2,6 toluene diisocyanate), 0.6 g ofhydroquinone monomethyl ether (MEHQ); 5.6 g of triphenyl-phosphite and0.18 g of dibutyl-tin dilaurate are added to this kettle. Upon heatingthe mixture to 30°-35° C., there is added dropwise 181.2 g ofhydroxypropyl acrylate, allowing the mixture to exotherm to 65° C. Thetemperature is maintained between 60°-65° C. for 11/2 hours at whichtime substantially all of the hydroxy groups are consumed, and the NCOcontent reaches 1.77±0.1 meg/g as determined by titration withdibutylamine. Thereafter, 752.4 g of melted poly (ethyleneglycoladipate) with a molecular weight of 1000 is added along with 0.15 g ofdibutyltin dilaurate catalyst. The reaction mixture is held at 65° to70° C. for approximately 6 hours until all the isocyanate groups areconsumed.

366.4 g of hydroxyethyl methacrylate and 0.4 g of hydroquinone are thenadded to this mixture. When the reaction mixture has become uniform andthe temperature has dropped to below 50° C., 237.8 g of solid maleicanhydride and 7.8 g of dibutyl-tin dilaurate are added. Slowly (overabout an hour) the reaction mixture is heated up to 55° C. to dissolvethe maleic anhydride. The heating is continued and held at 75° to 80° C.for approximately 6 hours until the maleic anhydride is completelyreacted, as indicated by the absence of 1845 and 1975 cm-1 peaks in anIR spectrograph. The final product thus obtained is a viscous liquidhaving viscosity of 5500 cps at 25° C. and acid group contents of 1.4meg/g.

EXAMPLE III

This example sets forth a process for making a hot melt polymercomposition.

A resin kettle is fitted with a stirrer, thermometer, drying tube and anaddition funnel. 129 g of hydroxyethyl methacrylate, 139 g ofhexamethylene diisocyanate, 0.4 g of hydroquinone monomethyl ether(MEHQ); 3.2 g of triphenyl-phosphite and 0.08 g of pyrogallol are addedto this kettle. Upon heating the mixture to 35°-40° C., there is added0.04 g of stannous octoate, allowing the mixture to exotherm to 85° C.The temperature is maintained between 70°-75° C. for 2 hours at whichtime substantially all of the hydroxy groups are consumed, and the NCOcontent reaches 2.44±0.1 meg/g as determined by titration withdibutylamine. Thereafter, 74.4 g of polyethylene glycol with a molecularweight of 1500 followed by 457.7 g of poly (ethylene-glycol adipate)with a molecular weight of 1000 is added along with 0.09 g of stannousoctoate. After the temperature reaches 60° C. there is added 0.12 g ofstannous octoate and the reation mixture is held at 65° to 70° C. forapproximately 6 hours until all the isocyanate groups are consumed.

22.7 g of maleic anhydride and 0.8 of hydroquinone and 4 g of dilutyltin dilaurate are then added to this mixture. Slowly the reactionmixture is heated up to 55° C. to dissolve the maleic anhydride. Theheating is continued and held at 70° to 75° C. for approximately 6 hoursuntil the maleic anhydride is completely reacted, as indicated by theabsence of 1845 and 1975 cm⁻¹ peaks in an IR spectrograph. The finalproduct thus obtained is a solid at 25° C. and has an acid content of0.29 meg/g.

EXAMPLE IV

This example sets forth the use of the polymer of Example III in a hotmelt photopolymerizable composition.

The hot melt formulation has the following composition:

    ______________________________________                                        Component          Percent By Weight                                          ______________________________________                                        Polymer of Example III                                                                           89                                                         Stearic Acid       4.5                                                        Pentaerythritol tetra-kis                                                                        3.5                                                        (B-Mercaptopropionate)                                                        Benzophenone       0.9                                                        Irgacure, Irgazin Blue,                                                                          2.4                                                        DC-193 Surfactant and                                                         Hydroquinone monomethyl                                                       ether                                                                         ______________________________________                                    

This composition is applied in about a 5 mil to a copper clad compositeboard by a drawdown bar at 55° to 60° C. Upon cooling the coatingsolidifies. A photographic negative of a desired circuit is thencontacted to the surface of this polymer. The negative is exposed for 90seconds to a medium pressure mercury vapor lamp at a distance to producean intensity of about 25 mille-watts/cm². The board is then sprayed withan aqueous sodium lauryl sulfate solution to remove the unexposedpolymer and selectively expose areas of the underlying copper cladding.The exposed copper cladding is removed by etching with a 3N hydrogenchloride-cupric chloride solution at 52° C. The copper is removed inabout 2 mins. The board is rinsed with water and the cured polymer isremoved by contact with a 5% aqueous sodium hydroxide solution at 55° C.The cured polymer is fully stripped in about 2 minutes exposing theunderlying circuit.

EXAMPLE V

This example sets forth the use of the polymer composition of Example IIas a screen-printable photocurable ink.

The screen-printable ink has the following formulation:

    ______________________________________                                        Component          Percent By Weight                                          ______________________________________                                        Polymer of Example II                                                                            79.40                                                      Hydroxyethyl methacrylate                                                                        0.98                                                       Irgacure           2.94                                                       Benzophenone       0.98                                                       Modaflow, Talc and Cabosil                                                                       8.50                                                       Ethylene Glycol    0.75                                                       Trimemethylol propane-tris-                                                                      5.95                                                       B-Mercaptopropionate)                                                         Chromophtal Blue   0.45                                                       ______________________________________                                    

This composition is coated onto a copper clad composition board througha screen bearing the desired circuit design. The board is then exposedto two 80 watts/cm medium pressure mercury vapor lamps which are 46 cmapart and spaced about 7 cm above the board. The ink quickly cures toform the solid acid stable resist. The exposed copper is removed byetching at 52° C. with a ferric chloride solution. The board is waterwashed and contacted with a 5% aqueous sodium hydroxide solution at 52°C. The solid cured polymer is removed in about 20 seconds to expose theunderlying circuit.

EXAMPLE VI

This example illustrates the use of the polymer of Example I in aphotographic imaging process.

The imaging composition has the following formulation:

    ______________________________________                                        Component          Percent By Weight                                          ______________________________________                                        Polymer of Example I                                                                             79.9                                                       Epoxy Acrylate     6.9                                                        Benzophenone       2.8                                                        Irgacure 651, Hydroquinone                                                                       1.6                                                        Monomethyl ether, Pyrogallol                                                  and Chromophlat Blue                                                          Modaflow           2.3                                                        Pentaerythritol tetra-kis-                                                                       6.5                                                        (β-Mercaptopropionate)                                                   ______________________________________                                    

This composition which has a Brookfield viscosity of 3,450 at 24° C., iscoated onto a copper clad circuit board blank in a thickness of about 2mils by means of drawdown. A negative of the desired circuit is thenplaced 10 mils above the liquid polymer surface and the negative isexposed to medium pressure mercury vapor light at an intensity of about25 mil-watts/cm². The board is then washed with a 5% sodium carbonate atroom temperature to remove the polymer which has remained liquid. Afterwater rinsing the exposed copper is removed by etching using a 3Nhydrochloric acid-cupric chloride solution at 52° C. The exposed copperis removed in about 1 to 2 minutes. The board is then water washed andcontacted with a 5% aqueous sodium hydroxide solution at 55° C. forabout 30 seconds. This solution removes the cured polymer to expose theunderlying circuit.

EXAMPLE VII

This example illustrates another use of the polymer of Example I in aphotographic imaging process.

The imaging composition has the following formulation:

    ______________________________________                                        Component            Percent By Weight                                        ______________________________________                                        The resin product of Example I                                                                     61.7                                                     Epoxy Acrylate       12.0                                                     Trimethylolpropane Triacrylate                                                                     7.1                                                      Hexanediol Diacrylate                                                                              4.8                                                      Pentaerythritol tetra-kis-                                                                         6.9                                                      (B-Mercaptopropionate)                                                        Modaflow             1.8                                                      Chromophtal Blue     0.5                                                      Pyrogallol           0.02                                                     Hydroquinone Mono-methyl ether                                                                     0.04                                                     Irgacure 651         1.95                                                     Benzophenone         2.91                                                     Triphenyl phosphite  0.38                                                     ______________________________________                                    

This composition which has a Brookfield viscosity of 4,500 at 24° C., iscoated onto a copper clad circuit board blank in a thickness of about 2mils by means of drawdown. A negative of the desired circuit is thenplaced 10 mils above the liquid polymer surface and the negative isexposed to medium pressure mercury vapor light at an intensity of about25 mil-watts/cm². The board is then washed with 5% sodium carbonate atroom temperature to remove the polymer which has remained liquid. Afterwater rinsing the exposed copper is removed by etching using a 3Nhydrochloric acid-cupric chloride solution at 52° C. The exposed copperis removed in about 1 to 2 minutes. The board is then water washed andcontacted with a 5% aqueous sodium hydroxide solution at 55° C. forabout 30 seconds. This solution removes the cured polymer to expose theunderlying circuit.

The foregoing examples have been set forth to further illustrate thepresent invention. However, even though the examples are set forth usingparticular materials other equivalent materials can be used. Forinstance in place of hexanediol diacrylate other diacrylates such astetraethylene glycol diacrylate, diethylene glycol diacrylate,triethylene glycol diacrylate, trimethylolpropane diacrylate andpentaerythritol triacrylate can be used.

Also in the foregoing examples the use of these polymer compositions hasbeen illustrated for plate resist and etch resist processes. However,these polymer compositions can also be used as solder masks. They aresufficiently stable to molten solder temperatures. In such a usage thecured liquid polymer can be applied by screen printing or by thetechnique of coating the whole board and using a photo tool toselectively expose areas of the circuit board to actinic light tosolidify the polymer in all areas except where solder is to be applied.In such a process any uncured polymer is removed and the exposed areascoated with solder. Usually after the solder is applied the curedpolymer is left on the board to serve as an insulative and protectivelayer.

We claim:
 1. A liquid polymer composition suitable for use as a photoresist comprising:(a) liquid polymer wherein the polymer consistseventually of a polymer having a single terminal alkene unsaturation atone end, a terminal carboxyl group at the other end, said carboxyl groupand alkene unsaturation being in a ratio of about 1 to 1 a molecularweight of about 250 to 10,000, and an acid content of about 0.1 to 4.0mille-equivalents/gram; and (b) an additive to control the viscosity ofsaid liquid polymer and to enhance the alkaline stripability of thecured liquid polymer.
 2. A liquid polymer composition suitable for useas a photo resist as in claim 1 wherein said polymer has the structure:##STR7## wherein R₁ is hydrogen, methyl or ethyl, R₂ is alkyl of from 1to 6 carbon atoms, R₃ is alkyl, aryl or alkylaryl, (PE) is selected fromthe group consisting of polyethers, polyesters and mixtures thereof, xis an integer of from 2 to 50 and R₄ is alkyl, alkene, aryl oralicyclic.
 3. A liquid polymer composition as in claim 2 wherein saidadditive has the structure: ##STR8## wherein R₄ is hydrogen, methyl orethyl, R₆ is alkyl of from 1 to 6 carbon atoms and R₆ is alkyl, alkene,aryl or alicyclic.
 4. A liquid polymer composition as in claim 2suitable for use as a photo resist which includes a photoinitiator forpromoting free radical generation.
 5. A liquid polymer composition as inclaim 4 suitable for use as a photo resist wherein said photoinitiatoris selected from the group consisting of benzophenone, acetophenone,acenaphthenequinone, o-methoxy-benzophenone, dibenzosuberone,anthroquinone hexanophenone and 2,2-dimethoxy-2,2 phenyl acetophenone.6. A liquid polymer composition as in claim 4 suitable for use as aphoto resist which includes chain bridging agents selected from thegroup consisting of multifunctional acrylates and thiols.
 7. A liquidpolymer composition as in claim 6 suitable for use as a photo resistwherein said acrylate is hexanediol diacrylate and said thiol ispentaerythritoltetra-kis-(B mercaptopropionate).
 8. A liquid polymercomposition as in claim 4 suitable for use as a photo resist wherein R₃is aryl and R₄ is ethylene.
 9. A liquid polymer composition as in claim4 suitable for use as a photo resist wherein in the structure of saidadditive R₆ is ethylene.